1. Field of the Invention
The present invention relates to a laser diode formed on a semiconductor substrate and specifically relates to a surface emitting laser diode emitting light in a direction perpendicular to the semiconductor substrate.
2. Description of the Related Art
Semiconductor lasers and the like include laser diodes each having a plurality of nitride compound semiconductor layers and the like stacked on a semiconductor substrate. Among such laser diodes, a laser diode having a structure emitting light in a direction perpendicular to the semiconductor substrate is called a surface emitting laser diode, and a surface emitting laser diode including a resonator arranged perpendicularly to the semiconductor substrate is called a “vertical cavity surface light emitting laser (VCSEL)”. The surface emitting laser diode has excellent characteristics such as low threshold operation, emission of a circular narrow beam, and easy production of a two-dimensional array and is applied to various fields such as high speed optical communications.
As an application example, if the beam polarization of the laser diode can be controlled into a certain shape, the spot size of the output light can be made small. Accordingly, the possibilities of further applications to high density recording and reading optical pickup light sources are being examined. For example, a small spot size beam polarized in the optical axis direction can be obtained by condensing by use of an aperture only light which is polarized in a direction perpendicular to an optical axis direction and transmitted through edge part of a high NA lens.
However, such a method of transmitting light through a plurality of optical devices to generate light polarized perpendicularly to the optical axis direction and reducing the spot size of the generated polarized light by means of the aperture increases the size and cost of a laser generator.
Moreover, the VCSEL has a structure which includes a resonator layer sandwiched by distributed Bragg reflectors (DBRs) parallel to the substrate. Because of the structure including the DBR, the VCSEL has low heat radiation performance. Accordingly, an increase in power of the VCSEL needs to be suppressed, or the reliability thereof is degraded.